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  1. Free, publicly-accessible full text available March 1, 2024
  2. Abstract

    Lithium‐ion and sodium‐ion batteries (LIBs and SIBs) are crucial in our shift toward sustainable technologies. In this work, the potential of layered boride materials (MoAlB and Mo2AlB2) as novel, high‐performance electrode materials for LIBs and SIBs, is explored. It is discovered that Mo2AlB2shows a higher specific capacity than MoAlB when used as an electrode material for LIBs, with a specific capacity of 593 mAh g−1achieved after 500 cycles at 200 mA g−1. It is also found that surface redox reactions are responsible for Li storage in Mo2AlB2, instead of intercalation or conversion. Moreover, the sodium hydroxide treatment of MoAlB leads to a porous morphology and higher specific capacities exceeding that of pristine MoAlB. When tested in SIBs, Mo2AlB2exhibits a specific capacity of 150 mAh g−1at 20 mA g−1. These findings suggest that layered borides have potential as electrode materials for both LIBs and SIBs, and highlight the importance of surface redox reactions in Li storage mechanisms.

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  3. Abstract

    Since their discovery in 2011, the number of 2D transition metal carbides and nitrides (MXenes) has steadily increased. Currently more than 40 MXene compositions exist. The ultimate number is far greater and in time they may develop into the largest family of 2D materials known. MXenes’ unique properties, such as their metal‐like electrical conductivity reaching ≈20 000 S cm−1, render them quite useful in a large number of applications, including energy storage, optoelectronic, biomedical, communications, and environmental. The number of MXene papers and patents published has been growing quickly. The first MXene generation is synthesized using selective etching of metal layers from the MAX phases, layered transition metal carbides and carbonitrides using hydrofluoric acid. Since then, multiple synthesis approaches have been developed, including selective etching in a mixture of fluoride salts and various acids, non‐aqueous etchants, halogens, and molten salts, allowing for the synthesis of new MXenes with better control over their surface chemistries. Herein, a brief historical overview of the first 10 years of MXene research and a perspective on their synthesis and future development are provided. The fact that their production is readily scalable in aqueous environments, with high yields bodes well for their commercialization.

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  4. Abstract

    Here, a new family of 2D transition metal carbo‐chalcogenides (TMCCs) is reported, which can be considered a combination of two well‐known families, TM carbides (MXenes) and TM dichalcogenides (TMDCs), at the atomic level. Single sheets are successfully obtained from multilayered Nb2S2C and Ta2S2C using electrochemical lithiation followed by sonication in water. The parent multilayered TMCCs are synthesized using a simple, scalable solid‐state synthesis followed by a topochemical reaction. Superconductivity transition is observed at 7.55 K for Nb2S2C. The delaminated Nb2S2C outperforms both multilayered Nb2S2C and delaminated NbS2as an electrode material for Li‐ion batteries. Ab initio calculations predict the elastic constant of TMCC to be over 50% higher than that of TMDC.

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  5. Abstract

    A comprehensive study on the prototype solid solution phase carbonitride MXene Ti3CN is conducted using nuclear magnetic resonance, electron spin resonance, total and quasi‐elastic neutron scattering, combined with density functional theory‐based electronic structure and molecular dynamic calculations. The combination of experiment and theory lead toward rational atomic structural models of Ti3CN. The remnant Al ions from the etching process significantly tune the interlayer spacing, distinct from the more typical MXene, Ti3C2, prepared similarly. Neutron scattering indicates the surface terminations of Ti3CN display high oxygen and fluorine concentrations and rather low hydroxyl and hydrogen concentrations. Calculations show that the structure including both the residual Al ions and mixed surface terminations give the best agreement with the measurements. The water molecules in Ti3CN are highly immobile, in strong contrast to those in Ti3C2. The analysis of the electronic structure suggests that the nitride MXene displays higher conductivity than the carbides. The absence of hydroxyl groups in terminations, the solid‐solution in the anion sites, the remnants within layers, and immobile water altogether make the carbonitrides a unique series in the MXene family, implying a further exploration of their exotic properties and applications in energy storage.

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